Ms. Samples was one of the athletes who christened the first Obstacle Course Racing site in Massachusetts Wednesday night at Ski Ward.

"It's enjoyable," said John Rinaldo, managing partner of Elevated Training LLC, while frantically tending to some last-minute details before opening night Wednesday. Elevated Training is the Worcester-based company that opened the site.

Mr. Rinaldo and fellow general partner Jeff Turgeon are banking on the sports' popularity to make a go of it at Ski Ward. Billed as the fastest growing sport in the U.S., an estimated 3 million people finished an OCR event last year, more than all half-marathon and marathon finishers combined, according to outsideonline.com.

Mr. Rinaldo and Mr. Turgeon have invested $10,000 of their own money in the business and hope to break even in this first season, which runs every Wednesday from 5:30 p.m. to sundown through September.

The business partners have fitness backgrounds. Before Mr. Rinaldo's current job operating training courses for bars and restaurants, he was the head strength coach at Providence College.

Mr. Turgeon grew up in Worcester and works for the city organizing job training programs. He has a master's degree in recreation management and has deep roots as a player and administrator for the Worcester Rugby Club.

Mr. Rinaldo has a reputation as an entrepreneur and handles the business end of Elevated Training, while Mr. Turgeon is in charge of course logistics and management.

"We're all fitness enthusiasts," Mr. Turgeon said. "We all love various aspects of fitness. One of the things we started to get into were these obstacle course races. We've got a lot of friends that do them. We've done some, and realized there wasn't any place to train for it."

The Ski Ward course is just over two miles. That distance may give a false sense of security to the casual athlete, but every step of the way is running up and down steep hills dotted with obstacles.

"Let's go, you're off!" Steve Dunn said to the first group of six racers who sprinted away from the starting line. Mr. Dunn is part of a team of volunteers who lent a hand at last week's opening night. He and Mr. Turgeon are friends from their rugby days, and as a financial analyst, he's a "potential business partner."

Besides carrying 20-pound sandbags, 45-pound concrete blocks and wading through 4-foot-deep mud pits, racers scale a 7-foot wall, crawl on their bellies, do push-ups, run through tires placed on the ground, and scramble over an 8-foot-tall pyramid made of hay.

Racers often don't know what to expect when they step to the starting line. At Ski Ward, the course can change, and in ultra-demanding OCR events such as the Spartan and Tough Mudder, racers are often kept in the dark, not knowing what obstacles to expect.

"That's what I like about obstacle course racing," Ms. Samples said. "You go to a marathon, you know what you're doing. You go to a triathlon, you know what you're doing. You go to an obstacle course race, you have no idea what's coming up."

Maureen Pellizzari showed up Wednesday with her 13-year-old son, Alex.

The 48-year-old mother of two from Shrewsbury said she loves a challenge.

Forty-six minutes later, she crossed the finish line and Alex recorded it on his camcorder.

"My husband and (other) son are playing lacrosse, and they're not here, so (Alex) said, 'Let's videotape you so Daddy can see it,' " Ms. Pellizzari said. "Maybe we'll show it to Grandma and Grandpa."

David Catarius was officially the first to complete the course, and sprinted through the finish line in a blistering time of 21 minutes.

The 45-year-old customer service manager from Shrewsbury wasn't done. He was waiting for some friends, and said he would run the course two or three more times when they arrived.

Ms. Samples, an OTC veteran, sees the Ski Ward training course as an opportunity to get ready for the upcoming 14-mile Spartan Beast in Vermont.

"It's a good community," Ms. Samples said before finishing the Ski Ward course in 32 minutes. "It's a great total body workout. The atmosphere is really good. Everybody has a good time, whether you're a competitor or just doing it to finish."

Mr. Rinaldo and Mr. Turgeon talked for several years about teaming up to run a business and settled on obstacle race training. Mr. Rinaldo would ultimately like to open up several OTC training sites. Mr. Turgeon said the goal this first season is to have 40 to 50 runners every Wednesday night.

They're using social media to spread the word. Nine runners competed on opening night, and more than 70 tackled the course earlier this month, when Mr. Rinaldo and Mr. Turgeon opened the course to friends and family.

Elevated Training's Facebook page displays 51 "likes," but the partners know it takes time to build a business.

As he helped organize volunteers, constantly checked his smartphone, and checked in racers at the registration table, Mr. Rinaldo summed up the spirit on opening night.